1. Field of the Invention
The present invention relates to an image pickup apparatus and, more particularly, to an exposure control apparatus.
2. Related Background Art
FIGS. 1A and 1B are block diagrams showing the arrangement of a conventional image pickup apparatus. Referring to FIGS. 1A and 1B, the image pickup apparatus comprises an imaging lens group 1 for an object image, an aperture mechanism 2 such as an iris for controlling the incident light amount, an image pickup element 3 for photoelectrically converting incident light, an iris detection unit 4 comprising, e.g., a Hall element for detecting the state of the aperture mechanism 2, a driving motor 5 such as an IG meter for driving the aperture mechanism 2, an image pickup element control circuit 6 which controls the image pickup element 3 to read out a photoelectrically converted signal, and controls the signal accumulation time, i.e., controls a so-called electronic shutter function, a sample and hold (S/H) circuit 7 for sampling a signal photoelectrically converted by the image pickup element 3, an auto-gain control circuit (to be referred to as an AGC circuit hereinafter) 8 for electrically amplifying a signal, and a camera signal processing circuit 9 for performing processing of a signal such as gamma correction, color separation, color difference matrix, and the like, and thereafter, adding a synchronization signal to the processed signal to generate a standard TV signal. As the camera signal processing circuit 9, as shown in FIG. 13, an analog signal processing circuit 9a for performing processing in an analog signal state, or a digital signal processing circuit 9b for analog-to-digital converting a video signal, performing processing in a digital signal state, and thereafter digital-to-analog converting the processed signal is available. In this case, the analog signal processing circuit 9a is used.
The apparatus also comprises a video tape recorder (to be referred to as a VTR hereinafter) 10 for recording a video signal from the camera signal processing circuit 9 on a magnetic tape, an electronic viewfinder 11 for monitoring the video signal, an AE detection circuit 15 for gating an output signal from the AGC circuit 8 as needed, and performing photometry for exposure control, such as selective central area photometry, an exposure control circuit 16 for controlling the shutter speed of the electronic shutter controlled by the image pickup element control circuit 6, the gain of the AGC circuit 8, and the like, an iris driving circuit 17 for driving the aperture mechanism 2 in accordance with an output from the exposure control circuit 16, a gate pulse control circuit 18 for generating gate pulses used for gating an image area required for detection in the AE detection circuit 15, a program mode change unit 19 for selecting a program mode, and a system control circuit 24 for controlling the program mode.
The AE detection circuit 15 comprises a selective central area photometry circuit 15a, weighting circuits 15b and 15c, and an adder 15d. The exposure control circuit 16 comprises an exposure control operation unit 16a, an AGC control unit 16b, an electronic shutter control unit 16c, and an iris control unit 16d. The system control circuit 24 comprises look-up tables (LUTs) 12, 22, 32, and 42 corresponding to program modes 1 to 4, and an LUT data control unit 24a. Note that the AE detection circuit 15 and the exposure control circuit 16 constitute exposure control means.
The image pickup apparatus with the above-mentioned arrangement realizes photographing control system called a xe2x80x9cprogram modexe2x80x9d which sets a mode for selecting a plurality of control parameters such as exposure control parameters, white balance control parameters, gamma correction, aperture correction, and color suppression correction parameters as camera signal processing parameters, and the like under conditions optimal for the respective photographing conditions, under some typical photographing conditions, so as to allow optimal photographing operations in various places and various conditions.
An example of a program mode that places an importance on exposure control will be described below.
Control parameters for determining exposure include the aperture mechanism, AGC, electronic shutter, and the like, and the system control circuit 24 stores data, which are set in correspondence with objects and photographing conditions in units of program mode, in the form of LUTs, i.e., the LUT 12 corresponding to program mode 1, the LUT 22 corresponding to program mode 2, the LUT 32 corresponding to program mode 3, and the LUT 42 corresponding to program mode 4. The system control circuit 24 reads out data of an LUT corresponding to the program mode set by the program mode switch unit 19, and controls the respective parameters on the basis of the readout data, thus realizing the program mode.
For example, when the motion of an object is fast, the electronic shutter for controlling the accumulation time of the image pickup element 3 is preferentially set at high speeds, thus achieving a so-called xe2x80x9csport modexe2x80x9d which allows a photographing operation with a good dynamic resolution. On the other hand, when the aperture mechanism is preferentially set at the full-open side, and exposure control is performed based on other parameters, a so-called xe2x80x9cportrait modexe2x80x9d which can provide an effect of blurring the background image due to a small field depth, and is suitable for a photographing operation of a person is achieved. In this manner, photographing operations optimal for photographing conditions can be realized.
Furthermore, the AE detection circuit 15 controls the photometry distribution on the basis of the photometry area and detection position of a video signal for exposure control, which are set by the gate pulse control circuit 18, thus realizing an optimal photographing operation. For example, the AE detection circuit 15 can realize so-called average photometry which detects a whole image area, and performs exposure control, so that the detection signal from the whole image area has a predetermined level, as shown in FIG. 5A. Also, the AE detection circuit 15 realizes selective central area photometry which detects only a central portion of the image area, and performs exposure control, so that the detection signal from the image area has a predetermined level, as shown in FIG. 5B.
When the AE detection circuit 15 performs exposure control on the basis of detection data obtained by weighting detection data from the whole image area and the selective central area in the weighting circuits 15b and 15c, and adding the weighted data by the adder 15d at a predetermined ratio, exposure control based on a photometry method as a combination of the average photometry and selective central area photometry can be realized. By changing the weighting coefficients in correspondence with an object and a photographing condition in each program mode, optimal exposure control that can effectively utilize the merits of the respective photometry methods can be realized. For example, when a main object is illuminated with spot light, and its background portion is dark, or when a main object is irradiated with back light, the weighting coefficient of the selective central area photometry is increased. On the other hand, when a proper exposure state is to be attained not only for a main object but also for a background object with a good balance, the weighting coefficient of the average photometry is increased.
Also, as shown in FIG. 5C, the frame is divided into division areas, image detection is performed in units of division areas, and the areas of detection data used in exposure control are limited or the weighting coefficient is changed in correspondence with an object or a photographing condition in each program mode, thus allowing flexible exposure control.
However, even in the exposure control based on the program mode, exposure control, which places an importance on the signal detection result obtained by detecting the brightness of a central portion under the assumption that a target object is present at the central portion of an image, is normally performed. For this reason, the signal detection area is fixed at the central portion, and when a target object of a photographer is offset from the central portion, optimal exposure control for the object cannot be attained.
The present invention has been made to solve the above-mentioned problems, and has as its first object to provide an image pickup apparatus which can perform proper exposure control with respect to a target object of a photographer.
In order to achieve the above object, according to a preferred aspect of the present invention, there is disclosed an image pickup apparatus comprising two-dimensional position selection means for selecting at least a portion of a video signal obtained from an image pickup element, exposure control means for controlling an exposure state of the video signal, and program mode control means, having a plurality of program modes which can be selected in accordance with a photographing condition and are respectively set with control parameters for controlling the exposure state, for outputting a control signal for controlling a position of a photometry area to be subjected to exposure in accordance with position information obtained from the two-dimensional position selection means, and supplying the control parameters set in the selected program mode and the control signal to the exposure control means.
According to another preferred aspect of the present invention, there is disclosed an image pickup apparatus, wherein the program mode control means can set the plurality of program modes for optimizing a camera signal processing state such as gamma correction, aperture correction, and the like, a white-balance state, a focusing state, and the like in addition to the exposure state by controlling one or a plurality of control parameters under a condition optimal for a photographing condition under one or a plurality of typical photographing conditions, and causes the exposure control means to perform optimal exposure control corresponding to the selected program mode.
According to still another preferred aspect of the present invention, input means such as a joystick, track ball, mouse, touch panel, or the like is used as the two-dimensional position selection means.
According to still another preferred aspect of the present invention, the control parameters include a parameter for controlling a size of the photometry area.
According to still another preferred aspect of the present invention, the control parameters include a parameter for controlling a moving range of the photometry area.
According to still another preferred aspect of the present invention, the control parameters include a parameter for controlling a moving range of the photometry area and limiting movement of the photometry area to an upper portion of an image pickup surface of the image pickup element.
It is the second object of the present invention to allow the photometry area in a frame to be movable, and to optimize the exposure control of the photometry area in correspondence with the photographing mode.
In order to achieve the above object, according to still another preferred aspect of the present invention, there is disclosed an image pickup apparatus further comprising means for setting an image detection area in first detection means for detecting the exposure state of the image area corresponding to the position selected by the two-dimensional position selection means, and setting a range for tracking the image detection area with respect to the selected position as control parameters associated with exposure control which is performed to track the detection signal of the image area corresponding to the position selected by the two-dimensional position selection means, second detection means for detecting an exposure state of an image area different from the first detection means for detecting the exposure state of the image area corresponding to the position selected by the two-dimensional position selection means at one or a plurality of positions, an d weighting mean s for multiplying detection signals from the first and second detection means with predetermined weighting coefficients, and wherein the program mode control means changes setting data of the detection area of the second detection means, setting data of the weighting coefficients to be multiplied with the detection signals of the first and second detection means by the weighting means, selecting data of exposure control parameters such as an aperture mechanism, auto-gain control, electronic shutter, and the like in the exposure control means, and setting data of response characteristics of exposure control, in correspondence with the program mode.
According to still another preferred aspect of the present invention, there is disclosed an image pickup apparatus an image pickup element having a photoelectric conversion function, an electronic viewfinder for displaying a video signal obtained from the image pickup element, viewpoint position detection means for detecting a position of a viewpoint of a photographer on a screen of the electronic viewfinder, exposure control means for controlling an exposure state of the video signal, and program mode control means, having a plurality of program modes which can be selected in accordance with a photographing condition and are respectively set with control parameters for controlling the exposure state, for outputting a control signal for controlling a position of a photometry area to be subjected to exposure in accordance with position information obtained from the viewpoint position detection means, and supplying the control parameters set in the selected program mode and the control signal to the exposure control means.
According to still another preferred aspect of the present invention, there is disclosed an image pickup apparatus further comprising means for setting an image detection area in first detection means for detecting the exposure state of the image area corresponding to the position detected by the viewpoint position detection means, and setting a range for tracking the image detection area with respect to the selected position as control parameters associated with exposure control which is performed to track the detection signal of the image area corresponding to the position detected by the viewpoint position detection means, second detection means for detecting an exposure state of an image area different from the first detection means for detecting the exposure state of the image area corresponding to the position detected by the viewpoint position detection means at one or a plurality of positions, and weighting means for multiplying detection signals from the first and second detection means with predetermined weighting coefficients, and wherein the program mode control means changes setting data of the detection area of the second detection means, setting data of the weighting coefficients to be multiplied with the detection signals of the first and second detection means by the weighting means, selecting data of exposure control parameters such as an aperture mechanism, auto-gain control, electronic shutter, and the like in the exposure control means, and setting data of response characteristics of exposure control, in correspondence with the program mode.
With the above-mentioned arrangement, since photometry is performed for the position of a main object selected by a photographer, and exposure is performed in correspondence with the photometry result, the main object can be optimally exposed without being influenced by light from a portion other than the main object. Upon combination with program mode control, an optimal image can be obtained in correspondence with an object and a photographing condition.
With the above-mentioned arrangement, when a photographer looks into the electronic viewfinder and watches a main object, photometry can be automatically performed for the position of the main object, and exposure is performed in correspondence with the photometry result. Therefore, the main object can be optimally exposed without being influenced by light from a portion other than the main object. Upon combination with program mode control, an optimal image can be obtained in correspondence with an object and a photographing condition.
Other objects and features of the present invention will become apparent from the following description of the specification taken in conjunction with the accompanying drawings.